1. Field
A semiconductor memory device and, more particularly, a semiconductor memory device having a precharge control circuit and an associated precharge method that reduces current consumption in a continuous writing operation.
2. Related Art
A semiconductor memory device repeatedly performs read and write operations. The read operation outputs data from a selected memory cell to circuitry external to the device. The write operation stores data, often received external to the device, in a selected memory cell.
A semiconductor memory device requires a precharging circuit for precharging input and output data lines to perform operations subsequent to the read or write operations.
The precharging circuit precharges input and output data lines responsive to the precharge control signal, including during continuous data write operations. That is, the precharging circuit precharges the input and output data lines between successive write operations.
FIGS. 1 and 2 are operation timing diagrams for precharging an input and output line in a continuous write operation in a semiconductor memory device having a double data rate (DDR) function. FIG. 1 is a timing diagram for controlling precharging an input and output line in a semiconductor memory device having a 4-bit prefetch structure for writing data having a burst length corresponding to 4 when a write command is continuously applied. FIG. 2 is a timing diagram for controlling precharging an input and output line to write data having a burst length corresponding to 8.
The DDR function refers to outputting data on both rising and falling edges of an external clock.
As shown in FIG. 1, an external clock signal Ext CLK and a first write command WR1 are applied. A second write command WR2 is applied two cycles from the external clock signal Ext CLK subsequent to the application of the first write command WR1 after a second write command WR2 is applied. The first and second write commands WR1 and WR2, respectively, enable the semiconductor memory device to perform the write operation. The first and second write commands WR1 and WR2 are applied in synchronization with the external clock signal Ext CLK.
When the first write command WR1 is applied synchronous to a pulse 0 of the external clock signal Ext CLK, a column select line enable signal CSL En CLK, pulse A is enabled a predetermined time after rising edge of the pulse 0. The column select line enable signal CSL En CLK, as its name suggests, enables a column select line CSL. The delay of the column select line enable signal CSL En CLK depends on write latency.
In response to a rising edge of the pulse A, a precharge control signal IOPR for controlling the precharge of the input and output line is disabled and the column select line CSL is enabled.
As a result, data is written via the input and output line responsive to the first write command WR1. A column select line disable signal CSL Dis CLK, pulse C, is enabled responsive to a rising edge of pulse 1 that follows pulse 0. The column select line disable signal CSL Dis CLK disables the column select line CSL. Responsive to a rising edge of the pulse C, the column select line CSL is disabled and the precharge control signal IOPR is enabled to precharge the input and output line.
After two external clock signal Ext CLK cycles, the second write command WR2 is applied synchronous with pulse 2 without any other command being applied after the first write command WR1. As the second write command WR2 is applied, the column select line enable signal CSL En CLK, pulse B, is enabled responsive to the rising edge of pulse 2. The delay of the column select line enable signal CSL En CLK depends on write latency.
Responsive to a rising edge of the pulse B, the precharge control signal IOPR is disabled and the column select line CSL is enabled.
As a result, data is written via the input and output line responsive to the second write command WR2. The column select line disable signal CSL Dis CLK pulse D, is then enabled responsive to a rising edge of pulse 3 that follows pulse 2 responsive to a rising edge of the pulse D, the column select line CSL is disabled and the precharge control signal IOPR is enabled to precharge of the input and output line.
For a continuous writing operation, the semiconductor memory device of FIG. 1 performs the precharge of the input and output line responsive to the column select line disable signal CSL Dis CLK subsequent to the first write command WR1. The semiconductor memory device completes the precharge of the input and output line responsive to the column select line enable signal CSL En CLK subsequent to the second write command WR2.
The semiconductor memory device repeatedly performs the above-described operation even upon the application of, for example, a read command RD.
As shown in FIG. 2, when a first write command WR1 is applied synchronous with a pulse 0 of an external clock signal Ext CLK, a column select line enable signal CSL En CLK, pulse A, is enabled with a predetermined delay responsive to a rising edge of the pulse 0. As before, the column select line enable signal CSL En CLK enables the column select line CSL. The delay of the column select line enable signal CSL En CLK depends on write latency.
Responsive to a rising edge of the pulse A, a precharge control signal IOPR is disabled so that precharge the input and output line stops, and the column select line CSL is enabled.
As a result, data is in part written via the input and output line responsive to the first write command WR1. A column select line disable signal CSL Dis CLK, pulse C, is enabled responsive to a rising edge of pulse 1 subsequent to pulse 0. Responsive to a rising edge of the pulse C, the column select line CSL is disabled and the precharge control signal IOPR is enabled to precharge the input and output line.
The column select line enable signal CSL En CLK, pulse B, is enabled responsive to the rising edge of pulse 2 of the external clock signal Ext CLK with a determined delay. The delay of the column select line enable signal CSL En CLK depends on write latency.
Responsive to a rising edge of the pulse B, the precharge control signal IOPR is disabled so that the precharge of the input and output line stops, and the column select line CSL is again enabled.
As a result, data is then written to the input and output line responsive to the second write command WR2. The column select line disable signal CSL Dis CLK, pulse D, is then enabled responsive to a rising edge of pulse 3 that is a next cycle of the pulse 2. Responsive to a rising edge of the pulse D, the column select line CSL is disabled and the precharge control signal IOPR is enabled to precharge the input and output line.
After four cycles of the external clock signal Ext CLK, the second write command WR2 is applied synchronous with pulse 4 without other commands. As the second write command WR2 is applied, subsequent operations are performed similarly to that described previously.
As described above, in a continuous writing operation, the semiconductor memory device performs the precharge of the input and output line responsive to the column select line disable signal CSL Dis CLK subsequent to the first write command WR1. The device completes the precharge of the input and output line responsive to the column select line enable signal CSL En CLK subsequent to the second write command WR2. The device performs the write operation responsive to the second write command WR2.
FIG. 3 illustrates a precharge control circuit to generate a precharge control signal IOPR in semiconductor memory devices operating according to FIGS. 1 and 2.
As shown in FIG. 3, the precharge control circuit includes a latch made up of two NOR circuits NO12 and NO14. Each of the two NOR circuits NO12 and NO14 has two inputs and one output.
The first NOR circuit NO12 receives a column select line disable signal CSL D is CLK at one input. The second NOR circuit NO12 receives a column select line disable signal CSL Dis CLK at an output.
The second NOR circuit NO14 receives a column select line enable signal CSL En CLK at one input. The first NOR circuit NO12 receives a column select line enable signal CSL En CLK at an output. The output of the second NOR circuit NO14 is the precharge control signal IOPR.
In a semiconductor memory device as described above, the precharge of the input and output line is necessarily performed after read or write operations, unnecessarily increases current consumption. Accordingly, a need remains for an improved semiconductor memory device that reduces current consumption by adjusting the precharging of the input and output line. To reduce the current consumption, there exists a need for a semiconductor memory device capable of reducing current consumption by not performing the precharge of the input and output line in continuous writing operation.